Wireless sensor networks (WSNs) usually employ different ranging techniques to measure the distance between an unknown node and its neighboring anchor nodes, and based on the measured distance to estimate the position of the unknown node. This paper presents an effective Particle Swarm Optimization (PSO)-based Localization Scheme using the Radio Signal Strength (RSS) ranging technique. Modified from the iterative multilateration algorithm, our scheme is unique in adopting the location data of remote anchors provided by the closest neighbor anchors of an unknown node to estimate the unknown nodepsilas position and using the PSO algorithm to further reduce error accumulation. The new scheme meanwhile takes in a modified DV-distance approach to raise the success ratios of locating unknown nodes. Compared with related schemes, our scheme is shown through simulations to perform constantly better in increasing localization success ratios and decreasing location errors -- at reduced cost.